1. Field of the Invention
The present invention relates to a light source apparatus that detects a light emission intensity while generating light to be supplied to an endoscope by a light-emitting element.
2. Description of the Related Art
As a light source apparatus of illumination light to be irradiated from an endoscope to a subject, a xenon lamp or the like has been conventionally used. However, with a spread of an LED, a light source apparatus using a light-emitting element such as an LED has been put into practical use in view of low power consumption and durability.
An LED is a light source which emits a light of a narrower band, compared with the xenon lamp, or the like, which is capable of emitting a white light by itself. The LED therefore cannot emit a white light by itself, and three methods as shown below, for example, are known as methods for generating a white light using an LED or LEDs as a light source:
(1) a method of using a blue LED as an LED, irradiating a fluorescent body with the light emitted from the blue LED to output a yellow light, and generating a white light by mixing the blue light emitted from the blue LED and the yellow light emitted from the fluorescent body;
(2) a method of using a near-ultraviolet LED as an LED, irradiating a plurality of kinds of fluorescent bodies with the light emitted from the near-ultraviolet LED to output lights of a plurality of colors, and generating a white light by mixing the outputted lights of the plurality of colors; and
(3) a method of using a red LED, a green LED and a blue LED as LEDs, and generating a white light by mixing the red light emitted from the red LED, the green light emitted from the green LED and the blue light emitted from the blue LED.
Among the above-described methods, the methods (1) and (2) can be used only for simultaneous illumination for irradiating a subject with a white light itself. On the other hand, the method (3) can be used not only for simultaneous illumination but also for frame-sequential illumination in which the red light, the green light and the blue light are irradiated in a time-series manner.
When the method (3) among the methods is employed, color balance adjustment for bringing the light close to a purer white light by adjusting the ratio among the light emission intensities of the red LED, the green LED and the blue LED is performed as an adjustment at the time of factory shipment of a light source apparatus.
It is known that light emission intensities of LEDs change with the passage of time (change over ages). Description will be made on this point with reference to FIG. 4 related to the present application.
As shown in FIG. 4, the light emission intensities of the respective color LEDs decrease with time, for example, and the decrease degree differs for each color.
Thus, even if the color balance adjustment is performed at the time of factory shipment, if no further measure is taken, the color balance changes with time.
A technology therefore has been proposed in which sensors for detecting the light emitting luminance of the respective color LEDs are provided and color balance is readjusted at an appropriate timing on the basis of detection results obtained by the sensors. However, if the sensors are fixedly arranged on the optical path of the illumination light, the light amount of the illumination light which reaches a subject is decreased.
In order to solve such a problem, for example, Japanese Patent Application Laid-Open Publication No. 2010-158415 discloses a technology for performing detection by using leak lights which are not used as an illumination light. In the technology recited in the publication, a red LED, a green LED and a blue LED are made to emit light in a frame-sequential manner first and the light emission intensity is measured by one light-receiving section, and color adjustment is performed such that the output voltage from the light-receiving section with respect to each color becomes a reference voltage value for each color according to the brightness set by a user (See paragraphs [0020]-[0028], FIG. 1, FIG. 2, etc.). In the technology, the reference voltage value for each color is calculated such that the light emission intensities of the red light, the green light and the blue light becomes a constant ratio (See paragraphs [0027], [0028], etc.). In addition, it is disclosed that the light emitted from each of the red LED, the green LED and the blue LED is received at the light-receiving section to acquire information on the emitted light amount, and the driving amount and also the emitted light amount of each of the red LED, the green LED and the blue LED are accurately adjusted, in view of variation of the emitted light amount due to a change over the ages and a temperature change (See paragraph [0050] etc.).